I started my periods seven years ago, and after about two years they became pretty regular, and I very rarely missed one. However, now I've suddenly gone for four months without a period and I'm worried. I know I can't be pregnant because I'm not sexually active, so what else could be the problem?

Hi the_eye_collector,
Some of the reasons for amenorrhea (no menstrual cycle) aside from pregnancy, are stress, diet, malnutrition, (anorexia), hormone disturbances, ovarian dysfunction, endocrine dyfunction, etc. I would strongly suggest since your menstrual cycles have been essentially regular until now, and pregnancy is not an issue, that you have an evaluation by your physician to identify if an underlying disorder is present.
Sincerely,
Theresa Jones, RN